Their photographs were mounted on plastic heads, stuck on stakes, with Nazi military caps placed on top.

The show took place at a summer camp for pro-Kremlin youth groups in the Tver region outside Moscow, which was attended by Vladislav Surkov, the deputy chief of staff and the Kremlin's chief ideologue.

It was organised by youth groups including Nashi, or Ours, known for its provocative political installations.

"Unworthy successors to (former president Vladimir) Putin," the Moskovsky Komsomolets daily wrote of the organisers on Wednesday, pointing out that Alexeyeva's father died at the front in World War II.

"Calling ideological opponents monsters was fashionable in all authoritarian regimes," it wrote.

"For their next 'art happening' activists will probably use tar and feathers," it said, referring to a traditional method of mob punishment.

Nashi campaigner Marina Drokova told the Kommersant daily that the exhibition was organised by Stal, a youth group within Nashi.

The summer camp, which closed Wednesday, was partly sponsored by the sports, tourism and youth politics ministry.

Nashi announced late Tuesday that it would sue a Kremlin human rights advisor after she sharply criticised the exhibition in an interview with the Echo of Moscow radio station.

"I am frightened that these guys will come to power in a certain number of years," Ella Pamfilova, who heads a council to promote the development of civil society and human rights, said Tuesday.

"These creatures of some of our spin doctors have pledged their soul to the devil, I put it coarsely. They have burnt books," she said.

Nashi announced that it would sue Pamfilova for slander, demanding 500,000 rubles (16,500 dollars) in damages. It cited her phrase about burning books.